1. Field of the Invention
The invention is in the field of measurement of component concentration within a tissue. More particularly, the invention relates to a method and system for non-invasive measurement of the concentration of optically active components, such as glucose, in a body tissue.
2. Description of Related Art
Millions of people worldwide suffer from diseases, such as diabetes, that require them to frequently monitor their blood/urine components, such as blood glucose levels. Nowadays, diabetic patients measure their blood glucose levels by using a variety of invasive portable devices. Since the patients need to perform such measurements several times a day, the invasive blood measurements become a burden. In addition, the measurements are often expensive due to disposable tools, such as needles and prickles. As a result, various non-invasive devices have been developed. When used at home, the non-invasive measurement devices enable patients who suffer from diabetes to monitor and respond accordingly to fluctuations in blood glucose levels on a daily basis.
As an example, U.S. Pat. No. 5,687,721 to Kuhls discloses a device and method for non-invasively measuring the concentration of sugar in the blood of a human subject. The method includes generating a beam of monochromatic light, confining the light beam to a predetermined optical path to impinge on a preselected portion of the body of the subject, polarizing the light beam, and performing both a static extinction measurement using the monochromatic light and a dynamic polarization measurement using the polarized light to obtain a measurement of the concentration of sugar in the blood in the preselected body portion. However, according to U.S. Pat. No. 5,687,721 the determination of the concentration of glucose in the blood depends on an absorption coefficient of a test specimen, which in turn leads to significantly inaccurate results, due to an inability to precisely determine such absorption coefficient.
As another example, U.S. Pat. No. 6,775,564 to Peters etal presents a glucose measuring device for determining the concentration of glucose in intravascular blood within a body part of a subject. The device includes a light source having a wavelength of 650, 880, 940 or 1300 nm to illuminate the fluid. A receptor associated with the light source for receiving light and generating a transmission signal representing the light transmitted is also provided. A support piece is included for supporting the light source associated with the respective receptor. The support piece is adapted to engage a body part of a subject. Finally, a signal analyzer determines the glucose concentration in the blood of the subject. However, U.S. Pat. No. 6,775,564 presents a spectro-photometric analysis that relies on the principle that every compound has a unique “pattern” determined by the amount of light absorbed, transmitted, or reflected by the compound at various wavelengths. Unfortunately, the spectro-photometric analysis is only of limited usefulness when the density of the specimen is unknown. These limitations are present because the absorption of light (or the intensity of transmitted light) may be directly affected by these variable factors. Thus, relying solely on the absorption of light at various wavelengths does not yield a sufficiently accurate non-invasive method for analysis of bodily fluids.
U.S. Pat. No. 5,920,393 to Kaplan discloses methods and devices for determining the identity and concentration of constituent compounds within a test specimen. The methods are based on the principle that a specific compound in a specific concentration modifies a pattern of the incident polychromatic light in a manner that is recognizable. The device includes a polychromatic light source directed first through an incident light pattern generator and then through the test specimen. Reflected and transmitted light components then pass through a pattern recognition gating device that selects portions of the light for analysis by an array of detectors. However, in similarity to U.S. Pat. No. 5,687,721, the determination of the concentration of glucose in the blood depends on an absorption coefficient of a test specimen, which in turn leads to significantly inaccurate results due to an inability to precisely determine such absorption coefficient. According to U.S. Pat. No. 5,920,393, when the concentration of optically active component within a test specimen is increased, then the angular distribution of the light beam is changed. However, such change in the angular distribution can be caused because of a change in the absorption coefficient, and not just when said concentration is increased. As a result, using the method of U.S. Pat. No. 5,920,393 for determining the identity and concentration of constituent compounds within a test specimen is relatively inaccurate.
The given method and the system featured in the current invention assumes a possibility of making of an miniature device to be coupled to a body of a person for the continuous monitoring of glucose level in blood. The device serves with an insulin pump a system supporting appropriate glucose level.
Therefore, there is a continuous need to provide a method and system for accurately determining the concentration of an optically active component within a test specimen like a body tissue. Other objects and advantages of the invention will become apparent as the description proceeds.